Refraction. Light travels in straight lines; but when a ray travelling through one medium passes obliquely into another of either greater or less density it is bent at the point of incidence. This bending or breaking is called refraction. The apparent bend in a stick set sloping in a sheet of water is due to this phenomenon, as are also many mirages and other optical illusions.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Reformed Church * Regalia